Heretofore there have been attempts in which water is electrolyzed by the photoelectromotive force produced by titanium oxide (TiO.sub.2), but because the wavelength of the light that allows energy conversion with titanium oxide is about 420 nm or less, the energy conversion efficiency with respect to sunlight is very low, and this technology has not been put to practical use. Heretofore, technology to electrolyze an electrolyte with the photoelectromotive force of sunlight by means of a solar battery immersed in the electrolyte has appeared in U.S. Pat. No. 4,021,323 and in unexamined patent application publication H6-125210 [1994] relating to the present applicant.
The U.S. patent discloses a solar battery array in which a pn junction is formed on spherical crystals of silicon and a common metal electrode film is formed on these multiple spherical crystals (a micro photoelectric cell), and a photochemical energy conversion device is described in which such an array of solar batteries is immersed in an electrolyte, and a solution of hydriodic acid or hydrobromic acid electrolyzed by the photoelectromotive force of sunlight.
Unexamined patent application publication H6-125210 [1994] discloses an array of light receiving elements in which multiple spherical crystals are formed near the surface of a semiconductor crystal substrate in matrix form and integral with the semiconductor crystal substrate, a photoelectromotive force generation part including pn junctions is formed on the surface part of the spherical crystals, and individual front-surface electrodes and a common back-surface electrode are formed on these multiple spherical crystals; it also discloses a photoelectrolytic device that includes the array of light receiving elements.
But with the technology described in these two documents, the direction in which sunlight can be received is limited to one surface, making it difficult to increase the light utilization rate in making use of the light in a light space.
In forming a solar battery array and individually forming the electrode films on the array of light receiving elements, the size of the photoelectromotive force is determined by the number of serial junctions of spherical crystals on which a pn junction is formed, so the solar battery array and array of light receiving elements must be designed and fabricated for each photoelectrolytic device. This makes it difficult to reduce the cost of fabricating solar battery arrays and arrays of light receiving elements suitable for photoelectrolytic devices, and makes it difficult to fabricate solar battery arrays and arrays of light receiving elements of wide application suitable for photoelectrolytic devices of various types and sizes.
The inventor of this invention has done research on photoelectrolytic devices that employ spherical semiconductor devices (of diameter about 0.5-2.0 mm) that function as micro photoelectric cells (or micro photocatalysts). In a photoelectrolytic device of this kind, it is necessary to support many small-particle spherical semiconductor devices in an electrolyte arranged so they can receive light, and to surely separate the reaction products, but as yet no structure has been proposed for thus arranging and supporting a large number of spherical semiconductor devices.
The purpose of this invention is to provide a solar battery module for a photoelectrolytic device that makes use of multiple independent grain-shaped spherical solar battery elements. A further purpose of this invention is to provide a solar battery module for a photoelectrolytic device in which one can appropriately set the size of the photoelectromotive force. Another purpose of this invention is to provide a solar battery module for a photoelectrolytic device of superior generality that can be applied to various photoelectrolytic devices. Another purpose of this invention is to provide a solar battery module for a photoelectrolytic device that can receive sunlight from various directions.
Another purpose of this invention is to provide a solar battery module for a photoelectrolytic device that can prevent overvoltage at the electrolysis electrodes and can promote the separation of reaction products from the electrodes. Another purpose of this invention is to provide a solar battery module for a photoelectrolytic device that has electrolysis electrodes having a catalytic function. Another purpose of this invention is to provide a photoelectrolytic device in which the solar battery module for a photoelectrolytic device is applied.